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Alteon OS Application Guide
Chapter 8: Basic IP Routing
14542C4911, January 2007
Routing Between IP Subnets
The physical layout of most corporate networks has evolved over time. Classic hub/router
topologies have given way to faster switched topologies, particularly now that switches are
increasingly intelligent. GbE Switch Modules are intelligent and fast enough to perform rout-
ing functions on a par with wire speed Layer 2 switching.
The combination of faster routing and switching in a single device provides another service—
it allows you to build versatile topologies that account for legacy configurations.
For example, consider the following topology migration:
Figure 8-1 The Router Legacy Network
In this example, a corporate campus has migrated from a router-centric topology to a faster,
more powerful, switch-based topology. As is often the case, the legacy of network growth and
redesign has left the system with a mix of illogically distributed subnets.
This is a situation that switching alone cannot cure. Instead, the router is flooded with cross-
subnet communication. This compromises efficiency in two ways:
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